VERTEBRATE ZOOLOGY 



CHAPTER I 



FISHES 



AN ELASMOB RANCH FISH. THE DOGFISH 



Several species of dogfish are common along the Atlantic coast. 

 They are the smallest of the sharks, and feed upon other fishes and 

 upon crustaceans, mollusks, and carrion. The species which have 

 been used for the dissection on which this discussion is based 

 are the smooth dogfish (Eugaleus galeus) and the spiny dogfish 

 (Squalus acanthias). The latter animal is easily distinguished 

 from the former by the prominent spine which projects from the 

 anterior border of each dorsal fin. 



For purposes of dissection, however, any species of dogfish will 

 do as well as either of these. The common skate may also be used ; 

 it is a near relative of the dogfish, and although in external form 

 and appearance it is very different from that fish, in internal struc- 

 ture it differs very little. The main point of difference is the 

 structure of the pectoral fins, which in the skate are enormously 

 developed and are attached to the side of the body along almost 

 its whole length. 



Three specimens will be needed for a complete dissection : one 

 for the external form and the principal viscera, including the 

 heart, the brain, and the nerves i one for the blood vessels ; and 

 one for the skeleton. Large specimens will be necessary for the 

 study of the genital organs ; small ones are not mature sexually. 

 During the progress of the dissection the specimens should be kept 

 in a 5 per cent solution of formalin or in cold storage. 



The body of the dogfish is much elongated and nearly cylin- 

 drical. The head is dorsoventrally depressed, with a projecting 



